Hydrated lime (calcium hydroxide) is the lime recommended for preparing bordeaux mixture. Hydrated lime is sold under several trade names or may be prepared by slaking calcium oxide. Do not use other forms of agricultural lime to prepare sprays.
Prepared Hydrated Lime—calcium hydroxide or Ca(OH)2
Good-quality hydrated lime is recommended for making tank-mix bordeaux. The lime should be fresh, not carbonated by prolonged exposure to air. Prepared hydrated lime is stable. It is sold as “spray lime” or “builder’s lime” under several trade names.
Slaked Lime—calcium hydroxide or Ca(OH)2
Slaked lime is prepared by adding water to “quick” lime (also called hot, burned, or unslaked lime, all of which are calcium oxide). Slaked lime makes an excellent suspension and may be used to tank-mix bordeaux mixture, but slaking requires more time, effort, and containers than using prepared hydrated lime.
Other Limes
Agricultural lime (soil amendment lime).
Ground limestone consists of calcium carbonate and varying amounts of impurities.
Dolomitic lime consists of varying proportions of calcium carbonate and magnesium carbonate and some impurities.